The invention relates to a device for crimping of synthetic bundles or slivers of yarn.
It is based on devices that have been disclosed by German Utility Model DE 18 77 098 U, U.S. Pat. No. 2,862,279, or European Patent Disclosure EP 0 268 031 B1.
In the known devices, the rollers exert a normal to surface force on the entering yarn bundle or sliver. As a result of the corresponding frictional force, the bundle or sliver is pressed into the stuffing box. By contact pressure of the pressure plate against the material located in the stuffing box, the requisite counterforce to the frictional force acting on the rollers is generated. Moreover, a counterpressure acts on the pressure plate, arising from the restoring force of the compressed material in the stuffing box. This force is generally distributed unevenly over the length of the stuffing box and as a rule increases in the feeding direction. If the center point of the counterpressure forces does not agree with the engagement point of the resultant of the inherent weight of the pressure plate and the contact-pressure force that engages the pressure plate, then the reaction force required to maintain the equilibrium of forces of the pressure plate ensues between second roller and the pressure plate. This affects the normal to surface force exerted by the two rollers on the entering yarn bundle or sliver, because it is superimposed on the force exerted on the second roller.
In the stuffing boxes that can be found in the references listed above, the engagement point of the contact-pressure force is fixed. In EP 0 268 031 B1, it is located at the outlet of the stuffing box. The center point of the counterpressure forces is always located in the middle region of the stuffing box. In this device, a reaction force therefore always ensues between the pressure plate and the second roller. In the devices of the other two references listed above, the contact-pressure force engages the pressure plate in the region of the stuffing box. Once again, a reaction force that acts on the second roller is generally unavoidable. Only for a certain contact-pressure force does the engagement point described assure that no reaction force will act on the second roller.
For process-dictated reasons, if certain crimping properties or various materials for crimping are to be attained, the contact-pressure force must be adjusted to different values. Thus a device with a fixed engagement point can be selected, in such a way that no reaction force on the second roller arises, for only a single method. As soon as the contact-pressure force is adjusted, a reaction force ensues, which leads to a change in the normal to surface force. To attain the originally set normal to surface force, the force with which the second roller is acted upon must be varied. This variation is typically done by trial and error and is thus very expensive. The distribution of the counterpressure exerted by the trapped fiber material on the pressure plate depends on the operating state. For instance, it changes if there are fluctuations in yarn titer. This shifts the center point of the counterpressure forces. As a consequence, there is a variable reaction force over time. The resultant fluctuations in the normal to surface force acting on the yarn bundle or sliver traveling through impair the uniformity of the crimping.
From German Patent DE 2 716 024, a device for measuring the radial force acting on a roller bearing by means of elastically deformable members and an electrical signal transducer is known. These devices can be obtained under the designation "Kraftme.beta.lager" [Force Measuring Bearings] (Brochure entitled "Kraftaufnehmer fuir FMS-Bahnzugme.beta.- und Regelsysteme" [Force absorbers for FMS web tension measuring and regulating systems] published by FMS Force Measuring Systems AG, Oberglatt, Switzerland). In the aforementioned patent, reference is also made to other devices for measuring radial bearing forces.